LACONIA, N.H. (AP) – Sen. Marco Rubio said Monday that radical jihadists are using the Syrian refugee crisis as cover to send terrorists to the West and that it's impossible for the United States to vet some migrants from the region.

"They are trying to exploit the refugee crisis out in the Middle East to insert fighters into foreign counties," Rubio told a New Hampshire audience in response to a voter who said Americans are concerned with immigration from a national security perspective. "We can't ignore that."

The debate over President Barack Obama's plans to accept 10,000 refugees from Syria over the next year has escalated in the wake of the terrorist attacks in Paris, with many Republicans questioning whether the United States can adequately screen Syrian refugees. Rubio said that while it may be easy to vet a young orphan or a well-known priest, the United States has no way of knowing if someone has recently become radicalized.

"If someone was a recently radicalized (Islamic State) fighter, there's no database we have that would identify you as such," said the Florida lawmaker. "You have people that a year ago were fully Westernized who have become fully radicalized in three, six, nine months."

So far, there is little evidence that the Islamic State has sent fighters to the West among the mob of refugees. U.S. intelligence officials have said it's possible but they have seen no evidence. A Syrian passport was found among the rubble of the Paris attacks, but a top German official said he believed it was a fake.

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Rubio and several of his Republican presidential rivals have said it would be better to help refugees stay in the Middle East. He suggested creating "safe zones" in Syria so people do not have to leave their home country and said Middle Eastern nations must do more to aid refugees in the region.

"I think a better solution is one that the people from the Middle East would agree with: Make it easier for them to stay in that part of the world," Rubio said to applause from the crowd.